The present invention relates to a precursor composition of silicon carbide or, more particularly, to a composition useful as a precursor of silicon carbide fibers having improved spinnability into filaments with a remarkably increased tensile strength suitable for infusibilization and calcination under tension.
In recent years, various kinds of high-performance ceramic materials are highlighted in respect of their excellent mechanical strength and heat resistance, of which silicon carbide belongs to a class of the most important ones. Silicon carbide is, however, workable with extreme difficulties due to the very high hardness thereof so that various methods of fabrication have been proposed and developed depending on the forms of the desired shaped articles of silicon carbide including the sintering method of fine silicon carbide powders, vapor-phase growing method, liquid-phase growing method, method of using an organosilicon compound as a precursor and the like. When the desired silicon carbide article is in the form of fibers, an advantageous method generally undertaken for the preparation thereof is to spin an organosilicon compound as a precursor into a filament which is infusibilized and calcined at a high temperature into a fiber of inorganic nature composed of silicon carbide.
A class of the organosilicon compounds most widely used as a precursor of silicon carbide fibers includes various kinds of polycarbosilane compounds disclosed in, for example, Japanese Patent Publication Nos. 55-49621 and 57-26527 and Japanese Patent Kokai Nos. 56-74126, 57-56566 and 58-67730. These polycarbosilane compounds are spinnable into a filament which is converted into a silicon carbide fiber by the infusibilization and calcination at high temperatures. The green filament obtained by spinning the polycarbosilane, however, has a very low tensile strength of only about 500 g/mm.sup.2 and also is brittle and apt to be destroyed even by a very weak outer force to cause extreme difficulties in handling to reserve the filament form as such so that the polycarbosilanes are not free from great difficulties in continuous spinning and winding up of the green filament on a reel. In addition, green filaments of the polycarbosilanes cannot be subjected to the infusibilization treatment under tension so that no sufficient mechanical properties can be imparted to the silicon carbide fibers obtained therefrom.